X-ray tube



Oct. 26, 1937. R. THALLER 2,097,002

X-RAY TUBE Filed Oct. 5, 1934 5 a /er- Patented Oct. 26, 1937 UNITEDSTATES PATENT. OFFICE 4 x-aAY TUBE Application October-5, 1934, SerialNo. 747,103

In Germany-April '14, 1934' 3 ims. -1 F351 In all the knownconstructions of X-ray tubes the sharpness of the image at every pointo'fthe image carrier (photographic plate, fluorescent screen and thelike) depends onthe angle of inclination of the focal surface to the rayleading to said point. If, for example, the focal point is band-shapedthere is found in the X-ray photograph a noticeable and often verydetrimental falling off of sharpness from the middle towards the sidesand especially from the part of the image turned towards the anode tothe part fect if the focal surface makes an angle (gener--- ally betweenand 80) with the image plane.

Strictly speaking only a point focus or a spherical focal surface cangive an astigmatic image. Cir-- cular or annular foci with surfaceparallel to the image plane would produce practically anastigmatic.images but they would have .to be. very small in viewof'the totalsharpness which'de creases. with the size of focus. In order not todiminish too much the mean total sharpness of th'eimage linear foci havebeen used. Thiscon struction of tube however is very liabletoastigmatism'... The present invention relates to an X-ray tube of highoutput which will take a much higher load than the ordinary linear focustube and is not less satisfactory than the tubes with rotating anode forinstantaneous exposures, but which operates without astigmatism. In thisnew tube the surface which emits the X-rays is the outer surface, whichis uniformly bombarded with electrons, of a narrow cone made of a metalof high melting point, for example tungsten, having an apex angle ofabout 30 or less and having its axis at right angles to the image planein use. With this arrangement the effective imageforming focal surfaceappears substantially as a circle from every point of the image plane.

The invention is illustrated by way of example in the accompanyingdrawing.

Fig. 1 shows the X-ray tube with parts broken away.

Fig. 2 explains the action of the conical anode.

Fig. 3 shows a detail on a large scale.

Fig. 4 is a section along line 4-4 of Fig. 3 on a smaller scale,

Figs. 5 and 6 show diagrammatically other possibilities of arrangingauxiliary electrodes.

Figs. '7 to 9 show modified details.

According to Fig. 1 the conical anode a is secured to the anode supportA which is fixed in the-glass bulb R of" the X-ray tube in sucha mannerthat the cone axis is at right angles to the tube axis. In order thatthe conical anode a may be uniformly bombarded with cathode rays(electrons) several glow cathodes n surrounding the anode a andpreferably consisting of helically wound wire may be used which arearranged in a collecting device hprovided on the cathode support K.

an the diagrammatic explanatory Fig. 2, bis the edge ofrthe base of theeffective part of the, anode cone, c is the cone axis, the extension ofwhich inters'ects the image plane'g in the point e. The points in whichthe separate generating lines of the'cone a when produced beyond itsapex, intersect the image planeg form a circle 1 on this plane. From allpoints lying within the circle* I the'b'asecircle b' of the anode cone aisncompletely visible. The effective image-formirlglfocal surface 'isalways circular although the effectivelfocal surface is the conicalsurface seen from abov'et Since the base circle I) of the cone isparallel 'to' the image plane, the foreshorteni-ng of .thediame'ter das" observed from a pointon thecir'cle ids-very small. If, for example,the

vertical. angle or of the cone is 22*, the greatest foresho'rtening ofthe diameterdof the base of the cone as seen from a point on the circleI is the cone as seen from a point on the circle is less than 0.12 mm.with a cone having a base of,

for example 6 mm. diameter. Consequently the sharpness of the image ispractically uniform within the circle f. Furthermore the effectiveelectron emitting anode area corresponding to the conical surface ismore than five times the area of the base circle, thus procuring arelatively high radiating intensity as compared with the small apparentarea of the focal spot, which ensures a most sharp image.

In practice the cone need not have a straight generating line; this maybe somewhat curved, as shown in Fig. '7, so that the conical surface isfor instance a hyperboloid of revolution.

The cone may be cooled by radiation or by conduction. In the latter casethe cone may be embedded in a material of good conductivity, such ascopper. If the cone a is made hollow it may be cooled by means of amedium circulating rapidly in its interior. This modification is I shownin Fig. 8, according to which the anode support A is also hollow and atube q for supplying a cooling fluid is arranged within its hollow spacep and introduced with its end into the hollow space r of the anode a, sothat fluid may circulate as indicated by the arrows.

The collecting device illustrated consists of a drum-like metal casingh, the axis of which coincides with the axis of the cone. The plain wall2 of the casing which faces the base of the done has an opening is forthe conical anode a. The other end wall 7 of the casing has an opening mopposite the apex of the cone a for rays to pass out. The metal casinghis given a potential opposite to that of the anode. The opening it ismade so large that with a high vacuum no discharge can take placedirectly between the anode and the casing.

In the construction according to Figure 3 the axes of the helical wiresn which are in a plane with the axis of the cone a are parallel to theaxis of the cone. They may also be inclined to it so as to intersecteach other; for example they may be parallel to the opposed generatinglines of the conical surface, as shown in Fig. 9. Experiments have shownthat when the drum-like collecting device is correctly dimensioned theaxes may run parallel to the coneaxis without the bombardment of theconical surface becoming non-uniform, whether with a small emission(currents of a few mA) or with a, very high emission (currents'up to andover 1,000 mA).

The glow wires 11. are shown in Fig. 3 as being connected with the drumh of the supporting device at their left hand ends. In consequencethereof they are connected in series, if their free right hand ends areconnected with the terminals of the source of heating current, and havethe same potential as the collecting device. A connection in parallelmay be obtained, either without changing anythingin Fig. 3, byconnecting the free ends of the wires with one and the same terminal ofthe heating current source and the drum h. with the other terminal, orby passing the left hand ends of the wires n with proper insulationthrough the wall of the drum h and connecting both ends of each wiredirectly with the terminals of the current source. In this case ofcourse the potential of the glow wiremay be different from that of thecollecting device.

conical surface of the anode and more particularly to. obtain a moreuniform bombardment of the cone surface.

When using only two diametrically opposite glow wires the drum h ispreferably given, as shown in Fig. 4, an oval cross-section with thelonger axis in the plane passing through the two glow wires. If morethan two glow wires are used the drum is preferably made of circularcross-section. 1

I claim:

1. Riintgentube comprising an envelope, an

anode having a focal portion in the form of .a cone, said cone having anapex angle of not more than 30, a collecting device in the form of ametal casing surrounding said cone and having a radiation openingaxially opposite'the apex of the cone, and a plurality of substantiallyequidistant glow cathode wires arranged within said metal casing andbetween its shell and said anode cone and extending longitudinally ofsaid cone. 2.'R6ntgen tube as claimed in claim 1, comprising two glowcathode wires the axes of which lie approximately in a plane with theaxis of the anode cone, and a plurality of auxiliary electrodes alsoarranged within said metal casing between its shell and the anode coneand also extending longitudinally of the cone.

3. Rontgen tube as claimed'in claim 1, comprising two glow cathode wiresthe axes of which a lie .approximately in a plane with the axis of thecone, said metal casing being of oval cross-sec tion with the longeraxis coinciding approximately with the common plane of the cone axisand'the glow .wire axes.

' RUDOLF II-IAlL-LER.

